1. Field of the Invention
The invention relates to a grinding operation control and, more particularly to a grinding method and grinding machine with which a change in the outside diameter of a grinding wheel during grinding is measured to control a grinding operation.
2. Discussion of Background
During grinding, the outside diameter of a grinding wheel changes due to wear of the grinding wheel caused by grinding or a repair of a grinding layer of the grinding wheel. Detecting the amount of change in the outside diameter to control a grinding operation based on the detected change amount is indispensable for improving grinding accuracy and grinding efficiency. Japanese Patent Application Publication No. 11-277428 (JP-A-11-277428) describes a technique of calculating the outside diameter of a grinding wheel by measuring a surface position of a grinding portion of the grinding wheel using a touch probe, as a method of measuring the outside diameter of a grinding wheel. In addition, Japanese Patent Application Publication No. 5-104407 (JP-A-5-104407) describes a technique of measuring wear of a grinding wheel by an ultrasonic measuring method.
According to the technique described in JP-A-11-277428, the outside diameter of the grinding wheel is calculated through a grinding wheel measuring process that includes grinding a transfer pin and measuring the surface position of the transfer pin using a touch probe held by an arm made of a low thermal expansion material. Therefore, a measuring process is required and, as a result, the rate of operation of a grinding machine decreases. In the technique described in JP-A-5-104407, the amount of wear of the grinding wheel is measured on the basis of a change in the distance between the surface of the grinding wheel and an ultrasonic sensor head. Therefore, a change in the distance between the installation position of the ultrasonic sensor head and the rotation center position of the grinding wheel is also incorporated in change in the amount of wear. As a result, an error may be caused. Particularly, it is difficult to suppress a change in the distance due to the thermal expansion of a component resulting from a temperature change. In principle, a change in the distance may be suppressed by using a low thermal expansion material to form a component or keeping an ambient temperature constant. However, an expensive material or a temperature controller is required.